Pipe-bending press

ABSTRACT

According to the invention a flat metal plate for the manufacture of pipe is first oriented generally horizontally on horizontally spaced and longitudinally extending supports. A longitudinally extending center tool is pressed down against the workpiece between the supports so as to downwardly plastically deform the workpiece while simultaneously a brace body is pressed with an upward force against the plate directly opposite the center tool so as to hold the plate in contact with the center tool. The center tool and brace body are then synchronously displaced downward relative to the supports with the plate clamped between the center tool and brace body.

FIELD OF THE INVENTION

The present invention relates to a pipe-bending press. More particularly this invention concerns a method of operating such a press to deform a planar plate into a U- or C-section shape for the manufacture of welded pipe

BACKGROUND OF THE INVENTION

The invention relates to a method of making welded pipe from metallic plate on a pipe-bending press, and to a pipe-bending press that is provided with a lower support tool in a base frame consisting of two adjacent supports that are at a spacing from each other, and an upper tool that can be moved vertically downward toward the lower supports and that is carried on a support that can be lifted and lowered and that extends the entire length of the metal plate so that it can apply a bending force to the plate sitting on the lower supports.

The transformation of metal plate into welded pipe includes several steps. First, the normally planar thick metal plate is bent by being supported along its two parallel outer longitudinal edges and pushed toward the supports along a midline, thereby imparting to the planar plate a U-section. This is typically done in two steps. In a third step, the outer edges of the U-section intermediate workpiece are bent inward toward each other, preferably so as to touch. This is done normally by pushing the intermediate workpiece through a plurality of arrays of rollers forming a shape increasingly corresponding to a closed circle. Finally the seam is welded from outside and in some cases also from inside, and the joint is machined smooth.

A generic O-press of this type in closed-frame construction mode has become known from U.S. Pat. No. 5,390,520. The vertically shiftable center tool is guided in the lateral uprights of the frame and connected via cardan joints to piston-cylinder units secured to horizontal beams bridging the uprights. The two lower support tools are carried on a row of further cylinders braced on crosspieces extending between the uprights, each lower cylinder being coaxial with one of the upper cylinders. The opposite piston-cylinder units are intended to compensate for bending of the frame under the considerable reaction load from deforming the thick plate workpiece, which load is lower toward the ends. Thus the pressures in the various cylinders has to be controlled individually, and even with the most sensitive control it is hard to prevent the workpiece from being bent irregularly, that is so that it is not of perfectly uniform cross sectional shape from one end to the other and also perfectly straight, which is needed. Since the structure supporting the various cylinders itself deforms from the desired perfect straightness, it is very hard to create a straight workpiece.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide an improved pipe-bending press and method of operating same.

Another object is the provision of such an improved pipe-bending press that overcomes the above-given disadvantages, in particular that imparts a perfectly rounded and straight shape to the plate workpiece.

Yet another object is to provide a method and apparatus for making large-diameter workpieces for the manufacture of welded pipe at high speed.

SUMMARY OF THE INVENTION

According to the invention a flat metal plate for the manufacture of pipe is first oriented generally horizontally on horizontally spaced and longitudinally extending supports. A longitudinally extending center tool is pressed down against the workpiece between the supports so as to downwardly plastically deform the workpiece while simultaneously a brace body is pressed with an upward force against the plate directly opposite the center tool so as to hold the plate in contact with the center tool. The center tool and brace body are then synchronously displaced downward relative to the supports with the plate clamped between the center tool and brace body.

In other words, with this method the metal plate is clamped during the entire bending process by a brace body that is pressed below against the lower face of the workpiece and therethrough against the upper tool. Thus as the workpiece is gripped or clamped between the upper tool and brace body or lower tool, the workpiece is steadily deformed from a planar shape to an arcuate shape.

By clamping the metal plate during the entire bending process, namely by means of the brace body and its actuator, which, according to an advantageous proposal of the invention in the center between the supports of the lower tool with its force application center at the level of the longitudinal axis of the mount of the upper tool, the metal workpiece plate never separates from the tools. No out-of-roundness of the pipe occurs, nor is an extension of the cycle time required, which improves productivity.

A pipe-bending press that is especially suitable for performing the method in accordance with the invention has, underneath the lower tool aligned with the level of the longitudinal axis of the mount of the upper tool, a brace body engageable upwardly with the metal plate. The metal plate thus is clamped at several points, namely on the upper tool that has a width of a size corresponding to the spacing between the two supports of the lower tool, and the two supports of the lower tool that are at a distance from each other, as well as against the brace body that bears upward against the workpiece center, continually lifting or pressing the metal plate against the lower face of the upper tool that has curved shape.

According to a preferred embodiment of the invention, the brace body is connected with a piston rod of a hydraulic or pneumatic cylinder attached to a pressure accumulator, which makes simple application of the brace body force possible and thus clamping of the metal plate. Hereby, the pressure accumulator ensures an elastic, force-dependent, automatic resilience of the brace body in a simple manner at continual clamping of the metal plate, even during while the bending process is progressing, all under the management of a simple controller.

An alternative suggestion of the invention provides that the bending force that is exerted by the actuator onto the upper tool, which can be lifted and lowered, and the cylinder of the brace body to control the counter force that depends on the bending force by means of lowering movements of the brace body over a measurement and control device, are connected with each other. Optionally, path-dependent control can be used.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a side schematic view illustrating the invention at the start of a bending operation; and

FIG. 2 is a view like FIG. 1 at a later stage of the operation.

DETAILED DESCRIPTION

As seen in FIG. 1 a planar metal plate 1 with parallel longitudinal edges is positioned for deformation into a open seam tube is set on two supports 2 a and 2 b set at a transverse spacing from each other and forming a lower tool. A broad upper tool 4 has a part-cylindrical lower surface 3 centered on an axis lying in a vertical plane 12 and is carried on a vertically displaceable horizontal mount 5 that is formed by a rigid beam and that can be raised and lowered by a schematically illustrated actuator 6 fixed to a machine frame 14.

For clamping the metal plate workpiece 1 during the entire deformation process, a hydraulic actuator 7 underneath the metal plate 1 is provided in the center between the supports 2 a and 2 b of the lower tool. It consists of a cylinder 8 fixed on the frame 14 and having a piston rod 9 carrying at its upper end brace body 10 vertically displaceable by the actuator 7 on the plane 12. The cylinder 8 is attached to a pressure buffer or accumulator 13 and bears on a lower face of the workpiece plate 1 at a central point 11 on the plane 12 of the mount 5 of the upper tool 4 (see FIG. 2). A controller 15 (FIG. 2 only) operates both the actuators 6 and 7.

Once the FIG. 1 position is reached, the upper actuator 6 is operated to push down the upper tool 4 while the lower actuator 7 is maintained under sufficient pressure to hold the workpiece 1 at point 11 tightly against the lower face 4 of the tool. The upper tool 4, which is of a transverse width equal to or slightly less than the clear distance between the two lower tools 2 a and 2 b, is moved downward as shown in FIG. 2 to impart to at least that portion of the workpiece 1 a shape corresponding exactly to that of the lower tool face 3. Since the workpiece 1 is at all times clamped between the tool 1 and the brace body 10, it will not shift transversely in the press and the resultant shape will be perfectly uniform.

The brace body 10 with the pressure accumulator 13 moves downward and acts as a virtual spring even though it is follows the bending process, while always bearing on the metal plate 1 and ensuring it remains in contact with the entire lower face 3 of the upper tool 4. As a result of the brace body 10 being maintained at the center at the location 11 of the action, a lifting off of metal plate 1 from upper tool 4 is avoided and thus the geometry or the roundness of the slot pipe that is to be formed is not changed disadvantageously. 

1. A method of bending a flat metal plate for the manufacture of pipe, the method comprising the steps of: orienting the plate generally horizontally on horizontally spaced and longitudinally extending supports; pressing a longitudinally extending center tool down against the workpiece between the supports so as to downwardly plastically deform the workpiece while simultaneously pressing a brace body with an upward force against the plate directly opposite the center tool so as to hold the plate in contact with the center tool; and synchronously displacing the center tool and brace body downward relative to the supports with the plate clamped between the center tool and brace body.
 2. The method defined in claim 1 wherein the center tool is equidistant between the supports and the brace body is aligned vertically in line with the center tool.
 3. An apparatus for bending a flat metal plate for the manufacture of pipe, the apparatus comprising: a frame; a pair of horizontally spaced and longitudinally extending supports, the plate being oriented generally horizontally on the supports; a center tool above and generally between the supports; upper actuator means for pressing the center tool down against the workpiece between the supports so as to downwardly plastically deform the workpiece; a brace body below and generally between the supports; lower actuator means for simultaneously pressing the brace body with an upward force against the plate directly opposite the center tool so as to hold the plate in contact with the center tool; and control means connected to the upper and lower actuator means for synchronously displacing the center tool and brace body downward relative to the supports with the plate clamped between the center tool and brace body.
 4. The apparatus defined in claim 3 wherein the lower actuator means includes a fluid-actuated piston/cylinder unit and a pressure accumulator connected thereto.
 5. The apparatus defined in claim 4 wherein the central tool has an arcuate and downwardly convex lower face.
 6. The apparatus defined in claim 5 wherein the lower face is part cylindrical.
 7. The apparatus defined in claim 4 wherein the central tool has a transverse width equal generally to a horizontal spacing between the supports. 